The combination of having a head injury and being exposed to the common pesticide/herbicide, paraquat has been found to increase the risk of developing Parkinson's disease by three times. Paraquat is one of the most widely used herbicides, typically used on crops to control weeds and pests. The chemical is also deadly to humans and animals. A person with an already compromised head injury can compound that injury greatly by being around this poison, to the point of getting Parkinson’s disease. The study was conducted by researchers at UCLA and published in the medical journal of the American Academy of Neurology.

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"While each of these two factors is associated with an increased risk of Parkinson's on their own, the combination is associated with greater risk than just adding the two factors together," said study author Beate Ritz, MD, PhD, of UCLA's Fielding School of Public Health. "This study suggests that the physiological process that is triggered by a head injury may increase brain cells' vulnerability to attacks from pesticides that can be toxic to the brain or the other way around, for example, chronic low dose exposure to pesticides may increase the risk of Parkinson's after a head injury."

The research team examined 357 people with Parkinson's disease and 754 people without. All lived in the agricultural heartland of central California. All participants were asked to report any head injuries they may have received which resulted in a period of unconsciousness for more than five minutes.

Those individuals with Parkinson's disease were twice as likely to have head a major head injury compared with people without the disease. Twelve (12) percent of Parkinson’s patients reported a major head injury and only seven (7) percent of non-Parkinson's individuals reported a major head injury.

Their exposure to the herbicide was determined based on a 500 meter area around their home and place of work. This was combined through use of GIS with data on paraquat that has been collected by the California Pesticide Use Reporting system.

Those with Parkinson's disease were found to be 36 percent more likely to have exposure to paraquat than those without.

This kind of correlation is too large to look past and deserves a serious look. Poisons used on crops to control weeds and pests have secondary adverse effects on health and society. Public health officials must determine if these negative effects outweigh the benefits.